The present invention relates to computer internal battery backups.
Electric Power
Standard alternating current (AC) power is generated by power utility companies. Utility-supplied power is subject to temporary loss due to a variety of reasons including but not limited to lightning induced surges on transmission lines, power plant failure, and downed transmission lines.
Effects of Power Failure on Electronics
Modern electronic devices rely heavily on integrated circuits (IC) for their operation. Most integrated circuits can be damaged by application of too much voltage or current to the IC. Power fluctuations may damage integrated circuits in electronic devices such as network routers, gateways, and hubs.
Loss of electric power (such as a blackout) can damage a computer or cause it to lose data. Very short (on the order of milliseconds) voltage dips and sags generally do not cause a computer to shut down or lose data. Most personal computers are designed to withstand voltage dips (brownouts) of about twenty percent without shutting down. Deeper dips or blackouts lasting for more than a few milliseconds may cause a computer to shut down. Any work that was not saved prior to shutdown is lost.
If the computer is writing to a disk during a power loss, the disk may be permanently damaged. These "head crashes" are the result of the disk drive's read/write heads coming into contact with the data storage disk.
Uninterruptible Power Supplies (UPS)
Uninterruptible power supplies provide backup power for the purpose of allowing electronic devices to continue to work during brief periods when no utility power is available. Additionally, uninterruptible power supplies may protect electronic devices by providing power conditioning to correct surges and/or sags in the power supply.
Uninterruptible power supplies are used in many computer installations such as network file servers, telecommunications equipment or other applications where a sudden loss of power would create an unacceptable and costly disruption of service. For example, there may be situations where data would be lost or corrupted if power failed during a data transfer. Perhaps the cost of a business shutdown due to the unavailability of a network device would be sufficient to justify the additional cost of an uninterruptible power supply for the network device. Thus, for various reasons there are numerous applications where an uninterruptible power supply is desirable and the number of these applications would increase substantially if the cost were reduced.
Originally, an uninterruptible power supply provided uninterrupted power because its output did not need to switch from line power to battery power. The battery was constantly and continuously connected to the system load. This type of UPS always supplied power from the batteries. The constant current drain from powering the load did not discharge the batteries because a large built-in charger was simultaneously charging them. When AC utility power failed, the charger stopped charging and the batteries discharged as they continued to supply power to the load.
Newer uninterruptible power supplies connect both the input utility power and the battery (typically through an inverter and transformer) to the load. When the utility power fails, the load switches to battery power. During this brief switching period, the load is connected to neither the main power supply nor the battery. To overcome this disadvantage, power supply transformers act as an energy storage system that supplies power while the load is being switched from utility to battery power and vice-versa.
Presently available uninterruptible power supplies most commonly are placed between the standard AC utility outlet and the AC utility plug of an electrical device (e.g. a computer) which must receive continuous electrical power. The typical UPS includes a battery for providing electrical energy in the event of a utility power failure, an AC to DC converter/battery charger, and an inverter for converting the battery's electrical energy from DC to AC when utility power is not available. The device being powered (for example, a computer's internal power supply) then receives the AC input from the uninterruptible power supply and in turn converts this to the various regulated and unregulated voltages required for the system.
FIG. 2 shows a prior art external uninterruptible power supply which in battery backup mode boosts the low battery voltages and generates a square wave AC output to feed into the AC input of a power supply.
The battery charger of the conventional UPS depicted in FIG. 2 converts AC power to DC power at approximately the battery voltage with a trickle charge being available to assure that the battery remains charged at all times. Typically the battery is a lead acid battery. The boost stage boosts the low voltage from the battery to an appropriate DC level. The inverter then reconverts the DC energy from the DC battery voltage back to an AC power supply approximating standard utility AC power. In the event of a power failure, the internal DC voltage from the AC to DC converter drops below the battery output voltage. This causes the battery to begin supplying AC power (by way of the inverter) to the device being powered (for example, a computer) in lieu of the utility AC power. The system proceeds with the battery supplying power until standard AC utility power is restored or the battery discharges. While such arrangements work satisfactorily, they are relatively expensive and inefficient. Such systems must work at relatively high power levels of typically two hundred to three hundred watts and are typically only 75 to 80 percent efficient. Consequently, substantial amounts of power must be dissipated within the uninterruptible power supply. Large and expensive components are therefore required to dissipate the resulting heat. In addition, the AC to DC converter, the inverter, and corresponding control circuits must be duplicated within the main power supply within the computer or other electrical device. The customer must therefore in effect purchase two power supplies; a standard device power supply plus an uninterruptible power supply.
FIG. 3 shows a prior art external uninterruptible power supply which in battery backup mode boosts the low battery voltages to a high DC voltage and feeds it into the AC input of a power supply. Note that this scheme differs from FIG. 2 in that the UPS inputs DC power, rather than AC, into the AC input of the main power supply and thereby eliminates the need for an inverter stage in the UPS. If the output of the UPS boost stage is set sufficiently high, the power supply's internal boost stage will automatically turn off. In an alternate embodiment, an external battery may be connected to the node between the UPS battery and boost stage. Note, however, that any additional battery would not be part of, nor charged by, the UPS.
FIG. 4 shows a prior art external uninterruptible power supply which in battery backup mode feeds the high voltage battery (typically in the range of 84VDC to 96VDC) into the AC input of a power supply or into a separate DC input of the power supply that connects to the power supply boost stage after the AC bridge of the power supply. This scheme differs from that shown in FIG. 3 in that the use of a high voltage battery allows the elimination of a boost stage in the UPS. In an alternate embodiment, the high voltage battery output can be switched directly into a separate DC input on the main power supply, thereby bypassing the main power supply AC input and bridge. As in the scheme of FIG. 3, the main power supply's boost stage will automatically turn off if the input DC voltage is sufficiently high.
FIG. 5 shows a prior art external uninterruptible power supply that generates matching DC outputs to the power supply that it is backing up. This UPS essentially is running in a redundant mode with the main power supply. This scheme differs from that shown in FIG. 4 in that the UPS DC outputs are connected directly to the main power supply DC outputs. A disadvantage of this scheme, as in the schemes of FIGS. 3 and 4, is that redundant circuitry is required because an AC to DC converter (in the battery charger) and corresponding control circuits must be duplicated within the main power supply of the computer or other electrical device.
In an alternate embodiment, an additional battery could be connected to the node between the UPS battery and DC-DC converter. Note, however, that any additional battery would not be part of, nor charged by, the UPS.
The UPS shown in FIG. 5 is similar to the UPS disclosed in U.S. Pat. No. 5,237,258 to Crampton. As can be seen, it is neither internal nor modular as defined in this application.
Computer Internal Battery Backups
Internal battery backups are not a novel idea. For example, computers have long had internal battery backups for the purpose of powering clocks and maintaining RAM contents. These usually are low-power disposable batteries suitable only for long-term trickle discharge. Internal battery backups therefore generally supply no power conditioning capability and are not capable of running an entire device, such as a server.
U.S. Pat. No. 4,860,185 to Brewer, for an integrated drop-in replacement computer power supply with UPS, discloses an UPS and power supply provided inside a common housing. However, the invention of Brewer seems to be restricted to computers. Additionally, the UPS of Brewer appears to not be modular in the sense that additional UPS modules cannot be added to extend the length of a battery backup period.
Network Node with Modular Internal Uninterruptible Power Supply
Disclosed herein is a network node with a modular internal uninterruptible power supply. Additional UPS modules may be added to a network node to increase the length of UPS operation when AC utility power is not available.
The disclosed innovations provide at least the following advantages: an ability to customize the length of UPS operation by adding additional modular internal UPS; higher efficiency because only one AC/DC power converter is required; higher reliability due to the low component count; lower cost due to the low component count; and no floor space is required for an external UPS because the preferred embodiment is internal to the device being powered.